608
FXUS21 KWNC 201803
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 20 2025

SYNOPSIS: Model ensembles favor a slow deamplification of the mid-level pattern
through week-2, resulting in few concerns from a hazardous weather perspective.
Early week-2, mid-level low pressure over the North Pacific may enhance surface
winds along portions of the California coast at times before this feature
weakens and drifts away from the area. A tropical cyclone may move northward
parallel to the East Coast early- to mid-week, but anything that develops looks
to remain several hundred miles offshore, limiting impacts to rough surf and
perhaps isolated high wind gusts along the immediate coast. Moderate to heavy
precipitation in the Northwest is not expected to reach hazards thresholds, nor
are wet and windy conditions across south-central and southeastern Alaska.

HAZARDS

Slight risk of episodic high winds for coastal portions of California from Cape
Mendocino to Point Conception, Sun-Mon, Sep 28-29.

DETAILED SUMMARY

FOR TUESDAY SEPTEMBER 23 - SATURDAY SEPTEMBER 27:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SUNDAY SEPTEMBER 28 - SATURDAY OCTOBER 04: Todays model solutions for
500-hPa heights indicate a progressive transition away from an amplified wave
train stretching from the North Pacific across North America to a much more
zonal pattern during the week-2 period, resulting in relatively tranquil
weather with few concerns with respect to the potential for hazardous weather
over the Continental United States. At the outset of week-2, most guidance
continues to depict a fairly deep trough off the West Coast, although the
European Ensemble (ECENS) mean is considerably weaker than the GEFS and
Canadian Ensemble (CANENS) means. This pattern, in addition to predicted
surface high pressure off the West Coast and adjacent surface low pressure over
the interior West, may result in a tight pressure gradient at the surface,
increasing the chances high winds along the immediate West Coast. A slight risk
of episodic high winds is posted for coastal portions of California between
Cape Mendocino and Point Conception for Sep 28-29, where the chances for wind
speeds exceeding both the 85th percentile and 25 mph appear maximized. The
deterministic models and both the GEFS and CANENS means depict periodic
enhanced winds in this region early in week-2. By mid-week, the mid-level
trough should be weakening and drifting away from the area, which should weaken
the surface pressure gradient sufficiently to end the risk of high winds.



In addition to enhanced winds, models show the mid-level trough establishing
significant moisture transport into the Northwest. This is likely to result in
periods of enhanced precipitation for much of the northwestern CONUS into the
middle of week-2. A few inches of precipitation may accumulate over the course
of the 7-day period over both coastal and higher elevation locations in western
Washington and northwestern Oregon. However, this is a favored region for
enhanced precipitation when there is mid-level troughing off the Northwest
Coast, so these amounts are not markedly atypical, and no hazard is posted.
Farther inland, models continue to forecast conditions too mild for much
snowfall except on the highest peaks, where totals will be climatologically
unremarkable.



Mid-level troughing near or south of Alaska is expected to produce one or more
surface storms near the Aleutians and/or into the Gulf of Alaska during week-2.
With high surface pressure expected west of the Contiguous United States
(CONUS), this set-up would favor increased surface winds and abundant moisture
transport from the North Pacific into south-central and southeastern Alaska,
which in turn would enhance chances for heavy precipitation across this region.
The ECENS, CANENS, and GEFS means all show over 4 inches of rain falling on a
large part of this area during week-2, along with periods of gusty winds.
However, this is the wettest time of the year in the region. Weekly normals
exceed 2 inches almost region-wide now, reaching as high as 6 inches in central
Southeastern Alaska along the immediate coast. The pattern responsible for the
climatologically heavy precipitation also favors stronger winds than are
typical for most other parts of the Continent. Given the climatology, neither
the forecast precipitation totals nor wind gusts would reach hazardous
thresholds.



Many of the deterministic models - in particular the ECMWF AIFS - bring a
tropical cyclone northward in the western North Atlantic parallel to the East
Coast during the early to middle part of the period. All models keep any
development several hundred miles offshore, so its likely that any impacts on
the CONUS will be limited to rough surf and possibly isolated occurrences of
strong wind gusts along the immediate coastline.

FORECASTER: Rich Tinker

$$